The present invention relates to a method of producing interlocking metal parts. More particularly it relates to a method of producing such metal parts which slide under pressure on one another.
Metal parts that slide under pressure on one another are used for example in fixing technology of expansible metal fixing plugs. Usually such a plug includes an expansible sleeve and an expander body which is drawn or driven into the expansible sleeve to anchor the latter. When for preventing corrosion the two parts of the expansible metal fixing plugs that slide on one another during anchoring are composed of the same stainless steel having an austenitic crystalline structure, then the two surfaces sliding on one another start to bind at high expansion pressures during the anchoring process. As a result, the operation of the expansible fixing plug is considerably impaired by the binding. In particular, such a fixing plug is unsuitable for use in the tensile zone, since in the enlargement of the drilled hole as a result of cracks forming cannot be compensated since the fixing plug lacks the ability to expand subsequently.
It is therefore conventional to manufacture the parts of the expansible metal fixing plug from steel of different crystalline structure. Since however they can be manufactured and supplied only in large numbers, this possibility is not practicable in most cases. Furthermore, adequate homogeneity in the crystalline structures of the steels which is effective in reducing the tendency to bind with sufficient reliability, is not achieved.
In order to avoid difficult machining of austenitic steels, it is known to manufacture in particular sleeve-shaped parts by powdered metal injection-molding method (MIM-method). For this purpose the powdered metal is mixed with the desired allowing additions present in powder form and plasticized in a heated kneader with assistance of polymeric organic binders such as waxes and plastics, and then granulated. Processing on conventional injection-molding machines is consequently possible. An injection-molding tool of a similar construction to a plastic material injection-molding tool is utilized as the mold. The injection-molded shaped bodies (preforms) are put into a binder-removing furnace to eliminate the binder. During the binder-removing process, the molecular change of the binder collapse as a result of thermal or chemical decomposition. At the same time, pre-sintering of the metallic shaped bodies takes place which imparts adequate stability to them. During sintering which is carried out in vacuum or under a protective gas, the metallic injection-molded parts receive their final material characteristics and shape. With this method it is therefore possible to use small amounts of different steels and to manufacture finished products.